| タイトル | Galactic civilizations - Population dynamics and interstellar diffusion |
| 著者（英） | Sagan, C.; Newman, W. I. |
| 著者所属（英） | Institute for Advanced Study|Cornell Univ. |
| 発行日 | 1981-06-01 |
| 言語 | eng |
| 内容記述 | A model is developed of the interstellar diffusion of galactic civilizations which takes into account the population dynamics of such civilizations. The problem is formulated in terms of potential theory, with a family of nonlinear partial differential and difference equations specifying population growth and diffusion for an organism with advantageous genes that undergoes random dispersal while increasing in population locally, and a population at zero population growth. In the case of nonlinear diffusion with growth and saturation, it is found that the colonization wavefront from the nearest independently arisen galactic civilization can have reached the earth only if its lifetime exceeds 2.6 million years, or 20 million years if discretization can be neglected. For zero population growth, the corresponding lifetime is 13 billion years. It is concluded that the earth is uncolonized not because interstellar spacefaring civilizations are rare, but because there are too many worlds to be colonized in the plausible colonization lifetime of nearby civilizations, and that there exist no very old galactic civilizations with a consistent policy of the conquest of inhabited worlds. |
| NASA分類 | SPACE SCIENCES (GENERAL) |
| レポートNO | 81A45692 |
| 権利 | Copyright |
| URI | https://repository.exst.jaxa.jp/dspace/handle/a-is/415327 |
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